1. Field of the Invention
The present invention is directed to an aerator, and more particularly, a thru-hull aerator adapted for being mounted through the hull of a boat for oxygenating a live bait well, the aerator provided with an air-release mechanism to prevent or clear air-lock of the aerator pump.
2. Description of the Related Art
When fishing from a boat, it is a common practice to bring along bait fish or aquatic organisms in tanks known as live wells. In order to keep the bait fish alive for many hours, or even days, an aerator must be provided to replenish the oxygen in the water as it is depleted by the bait fish. Several distinct types of aerators have been developed.
For example, there are United States patents drawn to aerators wherein water is sucked through a pump and sprayed out a distributor manifold in the form of small jets above the surface of the water (U.S. Pat. No. 3,822,498), aerator pumps which cause air to bubble up for the bottom of the container to thereby aerate the water, and U.S. Pat. No. 5,139,659 teaches an air-lift water pump, aerator and filter wherein bubbles travel up a water-lift tube, bringing along entrained water. Many aerators and aerator systems utilize centrifugal rotary bilge pumps which are well known in the art.
In addition, there are numerous ways in which an aerator may be utilized on board a boat. For instance, a "self-contained" aerator may be placed into a bait bucket, adapted cooler or recirculating live well. Often, larger or commercial fishing boats have aerators which employ thru-hull transom installations. These aerator systems pump water from outside of the boat into a live well, the live well typically having an overflow which allows excess circulating water to flow out of the live well. Typically, the thru-hull aerator includes a pumping means which includes a through-transom fitting mounted in the boat transom below the normal water line and the pump is mounted inside the boat on a fitting with a hose leading from the pump to the live well. Generally, the fitting is mounted below the planing surface so that the thru-hull fitting draws fresh water from outside the hull.
In aerators and aerator systems which employ centrifugal bilge-type pumps (which are not self-priming), air lock in the pump can be a frequent problem. Air lock can be a particularly significant problem in thru-hull aerator installations. If the supply of water through the thru-hull fitting is not adequate (i.e., when the water intake fitting rises above the water level or when rough water causes the water intake to be exposed to the air), a pocket of air develops in the pump impeller, the pump looses it's prime and becomes air locked. Once an air lock develops, the pump ceases to pump water, and this condition jeopardizes the bait fish in the live well. The back air pressure in the impeller pump output lines in combination with the pressure of the outside water at the intake scoop causes an air bubble to be held at the impeller, causing continuous air lock.
Typically, air lock is cleared from the pump by turning the centrifugal pump off thus releasing the back pressure of air and allowing the water in the pump outlet hose to descend back through the centrifugal pump, thereby forcing any trapped air out of the impeller chamber. The pump is then restarted, and in theory, but not always in practice, the pump resumes the normal pumping of water. An alternative means to "jump start" an air locked impeller, especially when the aerator is mounted in the boat transom, is to rapidly drive the boat in reverse thereby forcing water into the uptake fitting and pump chamber to clear the air lock. However, both of these methods are impractical in that they presuppose that the boat operator is aware that the pump has become air locked. Often, especially with a live well full of bait fish, the time lapse between the pump becoming air locked and its detection can mean the death of many bait fish.
Numerous attempts have been made over the years to invent an aerator which prevents or relieves airlock. One pump designed to prevent airlock, currently available on the market, is an "anti-airlock" pump manufactured by Rule. This pump incorporates a device which is designed to periodically detect whether there is air present at the pump impeller. If air is detected at the pump impeller, the device shuts the pump off in an attempt to relieve the air through the impeller output line. However, this device is of limited success in application since the device does little to proactively clear the airlock and the impeller pump may remain inactive for an extended period of time while the device tests for continued air lock.
U.S. Pat. No. 4,913,620 teaches a centrifugal water pump in which the pumping chamber is horizontally oriented and such chamber has two wall portions or sectors of different radii. One wall portion has a radius substantially the same as the outer most radial path of the impeller blades and the other wall portion has a radius substantially constant but slightly greater than the radius of the radical path of the impeller blades. Connecting the two chamber wall portions are terminal walls, one of which is located adjacent to the outlet port. A first deflecting wall directs the pumped water upward into the outlet port. A second deflecting wall breaks up any air and air bubbles and fills any space wherein air or air bubbles could collect. The device of Kusiak et al. is mechanically complex and in order to function properly the device requires the divider wall to create a positive and negative pressure (as opposed to a normal flow of water) which actually reverses the flow of water, thereby allowing any trapped air to escape.
U.S. Pat. No. 5,449,454 to Hickok teaches an apparatus for expelling gas from within a sealed container. The device of Hickok is particularly designed for use with canister-type aquarium filters, is mechanically complex and is not suited to a thru-hull orientation.
Finally, U.S. Pat. Nos. 5,213,718 and 5,275,762 teach aerators wherein an impeller draws a water and air mixture down through an upwardly directed impeller inlet into a cavitation zone (i.e., the centrifugal pump is mounted upside down compared to the normal operating position). When the centrifugal pump rotates, the vacuum formed in the cavitation zone by rotation of the impeller will draw air through the air tube into the cavitation eye where a portion of the air will be entrained in the water flowing through the vaned impeller and out the water flow directing means into the tank. Excess air drawn into the cavitation eye through the inlet tube can escape upwardly through the water inlet thereby preventing air locking of the impeller, as would occur if air were to accumulate in the cavitation zone of a centrifugal pump mounted in the "normal" pump operating position, with the water inlet opening downwardly. The pump preferably floats on the water with the air/water inlet for the centrifugal pump immediately below the surface. Such a system has a number of attendant problems. First, a centrifugal pump is designed to be operated in a certain orientation. The pump may be operated upside down near the surface for periods of time without damage; however, if operated upside down at depth for any length of time, air in the motor housing will exit through the seal between the motor shaft and the impeller, and water will enter the motor housing, thereby causing damage. Further, if the pump is operated on the surface, oxygenation of the water will occur near the surface of the tank, and the lower reaches of the bait well will not be aerated.
Further yet, if the pump is operated at depth, the design must permit escape of excess air out through the water inlet so as to prevent air locking of the pump, or to permit flooding and restarting of an air-locked pump. The design must thus anticipate the various depths at which the pump may be operated, and the air-escape parameters for each depth. Such a design can not optimize the air/water mixture for maximum oxygenation of the pump at every given depth. As a result of these design constraints, the oxygenation efficiency is adequate, but much less than optimal.
In view of the foregoing, it is an object of the present invention to provide an aerator which eliminates or minimizes the above-mentioned and other problems, limitations and disadvantages typically associated with conventional aerators, and to prevent air lock of the pump impeller while simultaneously providing an aerator which achieves a high level of oxygenation of the water in a live well.